This invention relates to an oral or mouth appliance and to a method of making the appliance.
This invention relates particularly but not exclusively to an oral appliance that is a sports guard for protecting the teeth of a user in contact sports such as boxing, football, gridiron and rugby. It will therefore be convenient to hereinafter describe the invention with reference to this example application. It is to be clearly understood however that the invention is capable of broader application. For example the invention also extends to an appliance that is an orthodontic appliance.
Customised sports mouthguards are known. Typically they are made by taking a mould or impression of a user""s mouth and then moulding the guard individually from this impression to fit the specific and unique mouth of the user. While these customised guards obviously fit well in the user""s mouth, it will be readily understood that this method of making sports guards is expensive as each guard is made to custom fit the user""s mouth. Mass produced sports guards often do not produce a close fit and the protection that they provide is reduced as a result. This has limited their acceptance in the market place despite a clear need for an efficacious mass produced sports guard.
A further limitation of existing custom made and mass produced sports guards is that they are relatively soft and they offer only limited protection to the front teeth. If a blow strikes the front of the mouthguard the guard tends to deform so that the brunt of the blow is borne by the front teeth. This makes the front teeth vulnerable to being damaged or dislodged. It would be better if the force was transferred to all the teeth and particularly through to the back teeth that are particularly firmly anchored to the jaw. This makes the front teeth vulnerable to being damaged or dislodged.
Clearly it would be advantageous if a guard could be devised that had the strength and rigidity to transfer the force rearwardly so that the force is spread over all the teeth and particularly the back teeth. Clearly it would also be advantageous if a guard could be devised that had the fit of a custom made guard but that was mass produced and easy to fit in a domestic environment.
It is an object of the invention to provide a sports guard that ameliorates at least some of the shortcomings of the prior art described above.
According to one aspect of the invention there is provided an oral appliance, comprising:
a base member made of polyethylene having a generally U-shaped form corresponding to the outline of the arch of a user, the base member having inner and outer flanges interconnected by a web that defines at least one channel within which a row of teeth of a user are received; and
a continuous layer of thermoplastic material that is EVA that surrounds and encases the base member and attaches to the base member whereby to define a teeth engaging element within each channel, the thermoplastic material being capable of being moulded and shaped to suit the arch and teeth of a user which are received therein by heating to a certain temperature.
Thus the appliance, eg sports guard, comprises a base member of polyethylene which provides a basic shape and rigidity encased within a layer of thermoplastic material EVA. The layer of thermoplastic EVA can be heated to a temperature at which it is soft and formable and then conformed to the shape of the arch and teeth of a user.
Preferably the layer of thermoplastic material extends continuously over the full surface area of the base member providing a full and uninterrupted cover of the base member without any spaces or openings.
The base member confers a suitable level of rigidity on the base member but does have some flexibility in the direction of length of the channel, eg from front to rear thereof, and this enables the guard to accommodate arches of varying width. In addition it exhibits a surprising level of affinity for the layer of EVA thermoplastic material that covers the base member. This bonding of the EVA layer to the polyethylene together with encasement of the base member within the layer of EVA provides a guard that resists delamination during use. This is a problem that has plagued previous efforts to use thermoplastics materials such as EVA in a mouth appliance.
The applicant has been the first to discover the surprising and unexpected affinity and compatibility that polyethylene has for EVA. The materials have the ability to flex in harmony with each other without delamination. They also remain together when subjected to some level of heating and cooling, eg to shape the EVA. The applicant has also been the first to come up with the idea of encasing the polyethylene base member in the EVA layer. Previously it was thought that satisfactory bonding of an EVA layer to a base member could only be achieved for applications that require some flexing by having a thermoplastic material as the base member, albeit of higher softening point than the EVA layer. The belief was that thermoplastic material would only be compatible with other thermoplastic material.
Typically the layer of EVA softens at a temperature of 90xc2x0 C. to 95xc2x0 C., eg by placing it in a glass of boiling water which is available in any domestic or office environment. The layer of thermoplastic material can then be shaped by placing it in the mouth of a user while it is still malleable and formable and then allowing it to set by letting it cool back to room temperature.
The layer of thermoplastics material may have a thickness of 1 mm to 4 mm, preferably 1 mm to 3 mm, eg about 2 mm.
A layer of thermoplastic material of this thickness ensures that the appliance is not overly bulky. When received in a user""s mouth it is possible for the user to talk reasonably easily. This is important as in many sports such as football users are required to talk to each other while playing.
The appliance may define only a single said channel that is an upper channel configured to fit over only the upper arch of the user and receive the upper teeth therein. Guards that receive only the upper arch and teeth are the most commonly used sports guards used around the world in contact sports.
Alternatively the appliance may define both an upper and a lower said channel that are configured to fit over the upper and lower arches of a user. Further alternatively the appliance may define a lower said channel configured to fit over only the lower arch of a user. However these configurations are less widely used than the upper arch guards described above.
The web of the base member may thicken in a direction rearwardly along each side thereof from the leading end or front of the base member. Preferably the web thickens in a direction rearwardly to a point spaced a short distance from the rear of the base member and then thins from the point to the rear end. This thickening fills in the space between the upper and lower teeth in an appliance with both upper and lower channels.
The appliance may include a tongue tag, eg centrally positioned, defined in the inner flange for correctly positioning the tongue of a user during use.
Further the appliance may define breathing apertures passing through the base member and layer towards the front of the appliance and broadly centrally in the appliance.
According to another aspect of this invention there is provided a method of making an oral appliance, the method including:
moulding a base member from polyethylene in a first moulding step in a first mould, the member having a generally U-shaped form corresponding to the outline of the jaw of a user and inner and outer flanges interconnected by a web that defines at least one channel within which an arch and associated row of teeth of a user are received; and
removing the base member from the first mould and placing it in a second mould having a larger cavity than the first mould and moulding a continuous layer of thermoplastic material that is EVA onto the base member so that the base member is encased by and enclosed within the EVA to form a teeth engaging element that can be formed and shaped to suit the mouth of a user, the layer encasing the polyethylene base member and being compatible therewith to form an integral body that resists delamination during use.
Thus the base member made of polyethylene is moulded in a first moulding step and then the layer of EVA is moulded onto the base member in a second moulding step. It is important that the polyethylene base member has sufficient rigidity not to move when it is exposed to moulding forces in the second moulding step. Applicant has found that polyethylene has sufficient rigidity to withstand the forces of the second moulding step. At the same time it has the rigidity to perform its function in use as a sports guard. It does however permit some flexibility in a longitudinal direction to accommodate user""s having arch sizes of varying width.
In a particularly preferred form the base member defines an upper channel within which the upper teeth of a user are received.
The first and second moulding steps may each comprise injection moulding processes. The base member may be injection moulded in a first die or mould defining the shape of the base member. Thereafter the base member is removed from the first die or mould and held in a specific position is a second mould or die defining the shape of the layer of EVA on the base member. It is important that the base member be held firmly in a stationary position in the die for the layer to be successfully moulded onto it. It is also important that the base member is sufficiently rigid not to flex or bend when it is exposed to the pressure of injection moulding the layer.
The second die or mould may include positioning elements such as pins that hold the base member securely in position.